My invention relates to a method of conveying plate-like objects or parts of very different thickness, especially circuit boards. It also relates to an apparatus for conveying plate-like objects according to my method.
In a horizontal continuous production process circuit boards are subjected to different treatments, e.g. brushing, etching, cleaning, and rinsing, and so forth.
In the process, the circuit boards are conveyed in a horizontal orientation through a plurality of treatment stations. One such assembly line comprises at least one activating station and one or two rinsing stations.
The conveying of the plate-like parts or objects typically occurs by a plurality of rollers, which are cylindrical or can comprise comparatively thin axles with individually mountable disks. The rollers are put in rotation by drive.
For treatment of the circuit boards with fluid, which is sprayed against the plate-like objects from above and below, the plate-like objects must be fed through the upper and lower rollers.
If they contact on the lower rollers, they can be lifted from these conveying elements by action of the spray pressure so that disturbances or interruptions of the conveying process occur. For guarantee of reliable transport, the upper conveying element can be similarly driven.
With the apparatus and method used currently the lower rollers are driven by bevel or cone gear pairs mounted or driven by a drive shaft running in the longitudinal direction of the apparatus. The drive gear on the upper rollers comprises a straight-toothed bevel on at least one end of the rollers. Thus, the bearings of the upper rollers are guided in vertical slots, so that the axial spacing can be adjusted to the different thicknesses of the circuit boards to be treated.
Because of the weight of the upper conveying elements, these upper conveying elements are continuously pulled downwardly.
The structure of the gearing between the upper and the lower roller is advantageously chosen so that with the standard thickness of the circuit boards to be treated an ideal axial spacing results.
For all other plate-like object thicknesses or while operating empty, the axial spacing is set incorrectly and the gear system does not operate optimally.
Recently however, the differences between the thinnest and the thickest circuit boards have increased. Particularly because of the ever more prevalent multilayering, both foil-like and also very thick circuit boards are to be treated with these machines. While the maximum thickness is now about 5 mm, from now on it will also be necessary to treat plate-like objects which are up to about a 10 mm thickness. This is no longer possible with the above-described performance of the gearing between the upper and the lower roller. Also, an adjustment may be necessary with the variable spacing between the upper and lower rollers. So that with the thickest plate-like objects the gears should still mesh properly, a correspondingly large module of the gear system must be chosen. This, however, is not possible, because then with the given maximum allowed outer- and/or pitch diameter, the smallest possible tooth number is not attained.